Legionella is a bacterium that can cause Legionnaires' disease. Which control measures are commonly used to reduce its growth in building water systems?

Legionella is a bacterium that can cause Legionnaires' disease. Which control measures are commonly used to reduce its growth in building water systems?

• A. Maintain hot water temperatures above 60°C (140°F), cold-water temperatures below 20°C (68°F), maintain chlorine residual, flush dead legs, and perform system cleaning.
• B. Disable all water features and reduce temperature controls.
• C. Rely on antibodies in water.
• D. Ignore maintenance and rely on natural dilution.

Answer: (A)

Key idea: controlling Legionella in building water systems relies on keeping conditions outside the bacterium’s preferred growth range and maintaining active system hygiene and disinfection. Legionella grows best in warm, stagnant water and within biofilms that can form in pipes and tanks. By keeping hot water well above 60°C, we create a temperature environment that hinders bacterial survival, while keeping cold water below about 20°C discourages growth in those portions of the system. Maintaining a residual disinfectant, such as chlorine, helps continuously inactivate any bacteria that are present as water moves through the system. Flushing dead legs and other low-flow areas prevents stagnation, which is where Legionella can multiply, and regular system cleaning helps remove biofilms and sediment that shelter bacteria. Together, these practices reduce the chance of Legionella multiplying and becoming aerosolized from outlets. Why the other ideas don’t fit: removing temperature controls or disabling features increases stagnation and removes critical protective factors; relying on antibodies in water isn’t a practical or effective control; and ignoring maintenance allows biofilms to develop and biomass to grow unchecked.

Key idea: controlling Legionella in building water systems relies on keeping conditions outside the bacterium’s preferred growth range and maintaining active system hygiene and disinfection.

Legionella grows best in warm, stagnant water and within biofilms that can form in pipes and tanks. By keeping hot water well above 60°C, we create a temperature environment that hinders bacterial survival, while keeping cold water below about 20°C discourages growth in those portions of the system. Maintaining a residual disinfectant, such as chlorine, helps continuously inactivate any bacteria that are present as water moves through the system. Flushing dead legs and other low-flow areas prevents stagnation, which is where Legionella can multiply, and regular system cleaning helps remove biofilms and sediment that shelter bacteria. Together, these practices reduce the chance of Legionella multiplying and becoming aerosolized from outlets.

Why the other ideas don’t fit: removing temperature controls or disabling features increases stagnation and removes critical protective factors; relying on antibodies in water isn’t a practical or effective control; and ignoring maintenance allows biofilms to develop and biomass to grow unchecked.